stars that crunch not only matter
but the space around it, bringing
time there to an end. "Time can
not be an ultimate category in
the description of nature," he
declares. "'Before' and 'after'
don't rule everywhere." A pio
neer in quantum theory, at home
measuring time by billionths of a
second or by billions of years,
Wheeler tests the edge of our
understanding. "We will first
understand how simple the uni
verse is, when we recognize how
strange it is."
One way to imagine space
time is with a cone of light
(above), each panel representing
space at a different moment. The
tip of the cone may be any point,
say earth at this instant. Events
can be divided into those whose
light has had time to reach us-
those within our cone-and
those about which we still have
no knowledge. As earth moves
through time from left to right,
our cone widens on each panel
of space like a spreading flash
light beam, sweeping events
into our "present," our
"now." We don't see a star
explode as a supernova, top of
middle panel, until thousands
of years later, when its light
has reached us to announce the
event, right panel.
So time is relative, change
able. Can it be reversed? No.
The second law of thermody
namics-which states that iso
lated systems move from order
to disorder- unequivocally
rules that out. Humpty Dumpty
won't ever put himself back
together again.
PAINTINGBY HOWARDKOSLOW;CONSULTANTS:ALAN
LIGHTMAN,MASSACHUSETTSINSTITUTEOFTECHNOLOGY,
AND CHARLESW. MISNER, UNIVERSITYOF MARYLAND
The Enigma of Time
119